PROJECT SUMMARY/ABSTRACT Despite important advances in the treatment of learning disabilities (LDs), the dominant approach to intervention?direct skills instruction?fails to meet the needs of 25-40% of LD students. This, combined with the heterogeneity of LDs, indicates the need to expand the framework for LD treatment with innovative approaches that target the specific needs of subgroups of LD students. This study addresses a subset of the LD population with a distinctive set of needs: students with comorbid difficulty across word reading & calculations. This LD subgroup experiences weaker outcomes in both reading & math and poorer response to reading & math treatment than do peers with difficulty in just 1 of these domains. This study is guided by an innovative Theoretical Framework, which identifies opportunities for strengthening early word reading & calculations in theoretically coordinated fashion for this understudied and underserved population. The aim of this Phase 1/2 Clinical Trial is to extend understanding about connections between early reading & math and investigate the mechanisms by which effects of coordinated treatment may occur (Phase 1) while also assessing short-term effects of coordinated treatment (Phase 2). Comorbid 1st-grade students are randomly assigned to 4 conditions, a control group, coordinated treatment across reading & math, reading-only treatment, & math-only treatment. We (1) test coordinated treatment?s short-term effects on reading & math outcomes, while assessing (2) whether improved reading skill serves as a mediator of coordinated treatment?s effects on math outcomes and whether improved math skill serves as a mediator of coordinated treatment?s effects on reading outcomes; (3) whether improvement in targeted cognitive processes mediates coordinated treatment?s effects on reading & math outcomes in similar ways; & (4) whether other associated cognitive processes moderate coordinated treatment?s effects on reading & math outcomes in similar ways. This study impacts science by deepening understanding about connections between early reading & math development and offering insights to guide future directions for accelerating the learning of students with these comorbid LDs. This study impacts clinical practice by addressing word-reading + calculations comorbid LDs in a theoretically coordinated manner, which should ease the logistical challenges schools face in providing multiple forms of intervention to students with comorbidity ? challenges that often mean these children do not receive treatment in both domains. The focus is highly relevant & significant because comorbid reading & math LDs are associated with long-term negative consequences, including problems with employment, health, social adjustment, & quality of life.